Why is my water heater leaking from the top or the relief valve?

Water near the top of a heater may come from a loose connection, a nearby pipe or the tank itself. Water discharging from the temperature-and-pressure relief valve is different: the valve is a safety device that may be responding to a real problem. Do not cap, plug or disable that valve. Keep children away from hot discharge, and turn off the unit using the manufacturer's safety instructions if it can be done safely. Note whether water appears only during heating or all the time. Have a qualified plumber check pressure, temperature and connections rather than assuming that a new valve alone solves it.